View source for Kermadec–Tonga subduction zone

{{short description|Convergent plate boundary that stretches from the North Island of New Zealand northward}}
[[File:Kermadec and Tonga Plates.jpg|thumb|Kermadec and Tonga plates]]
{{maplink|frame=yes|frame-align=right|frame-width=350|frame-height=500|frame-long=177.3|frame-lat=-33|zoom=4|raw={{Wikipedia:Map data/Kermadec-Tonga subduction zone}}
|text=Approximate surface projection of [[Australia plate]] and [[Pacific plate]] subduction in the South Pacific. {{Wikipedia:Map data/Kermadec-Tonga subduction zone/key}}
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The '''Kermadec–Tonga subduction zone''' is a [[convergent plate boundary]] that stretches from the [[North Island]] of [[New Zealand]] northward.  The formation of the Kermadec and Tonga plates started about 4–5 million years ago. Today, the eastern boundary of the Tonga plate is one of the fastest [[Subduction|subduction zones]], with a rate up to {{cvt|24|cm/year}}.<ref name=":1" /> The trench formed between the Kermadec–Tonga and Pacific plates is also home to the second deepest trench in the world, at about 10,800 m,<ref name=":2" /> as well as the longest chain of [[Submarine volcano|submerged volcanoes]].<ref>{{Cite web|url=http://www.stuff.co.nz/environment/72528515/kermadec-sanctuary-has-worlds-second-deepest-trench-30-underwater-volcanoes|title=Kermadec sanctuary has world's second deepest trench, 30 underwater volcanoes|website=Stuff|date=29 September 2015 |access-date=2017-06-09}}</ref>
==Geological setting==
At the northern end of the zone the vector of the Pacific plate collision with the [[Australian plate|Australian]] changes to north–south from east–west, to the east of [[Fiji]] and south of [[Samoa]]. A number of microplates exist between the two major plates and host various back-arc structures of which the largest are the volcanic [[Tonga–Kermadec Ridge]], the actively spreading [[Lau Basin]] and the [[Havre Trough]]. At the southern end there is a transition to the [[transform fault]]s of the [[South Island]] of [[New Zealand]].
===Subduction===
The Kermadec–Tonga subduction zone is a [[convergent plate boundary]] that stretches from the southwest of the [[Kermadec plate]] (northeast of [[New Zealand]]) to the northwest tip of the [[Tonga plate]], with the [[Pacific plate]] being subducted under both the Kermadec and Tonga plates. The Kermadec and Tonga plates are micro oceanic plates in the Pacific Ocean, bounded by the [[Australian plate|Australian]] and Pacific plates to the west and east respectively. The Kermadec plate begins at the northeastern part of New Zealand and stretches northward to its contact with the Tonga plate where the volcanic hot spot chain of the [[Louisville Ridge]] passed historically. The Tonga plate begins {{cvt|2500|km}} NNE of New Zealand and stretches northward,<ref name=":0">{{Cite web|url= http://swpacificplates.weebly.com/kermadec-tonga--niuafoou-plates.html |title=Kermadec, Tonga, and Niuafo'ou tectonic plates |last=Pare|first=Pier-Alexandre|website=Southwest Pacific Plates |access-date=27 September 2017}}</ref> until the plate ends bounded by the [[Niuafo'ou plate]] to the northwest and the Pacific plate to the northeast.
The [[Hikurangi Margin]] is the extension of the Kermadec–Tonga subduction zone further south down the east coast of the North Island.
The subduction process seems to be driven primarily by the excess weight of the cold/old oceanic plate entering the hot mantle of the Earth.<ref>{{Cite journal|last1=Garcia-Castellanos|first1=Daniel|last2=Torne|first2=Montserrat|last3=Fernàndez|first3=Manel|date=2000-05-01|title=Slab pull effects from a flexural analysis of the Tonga and Kermadec trenches (Pacific Plate)|journal=Geophysical Journal International|volume=141|issue=2|pages=479–484|doi=10.1046/j.1365-246x.2000.00096.x|issn=0956-540X|bibcode=2000GeoJI.141..479G|doi-access=free|hdl=10261/237992|hdl-access=free}}</ref>
===Transform faults===
The southern end of the subduction zone transitions to a right lateral-moving transform fault south of the North Island called the [[Alpine Fault]]. This transition involves very active and complex faulting through the south-eastern North Island and [[Marlborough fault system]]. Further south the subduction process is reversed in the [[Fiordland]] region of the South Island
===Trenchs===
The eastern boundaries of the Tonga and Kermadec plates constitute the [[subduction]] zone of the Pacific plate, characterized by a trench about {{cvt|2000|km}} in length. The trench is continuous, but has different names for different sections: [[Hikurangi Trough]], the [[Kermadec Trench]] and the [[Tonga Trench]]. The Tonga Trench is the second deepest trench in the world at about 10,800 m, with the deepest point, Horizon Deep, being the deepest point in the Southern Hemisphere and the second deepest point in the world, after the [[Challenger Deep]] in the [[Mariana Trench]].<ref name=":2">{{Cite web|url=https://www.ngdc.noaa.gov/gazetteer/|title=Undersea Features Gazetteer|publisher=National Geophysical Data Center|access-date=2017-06-09}}</ref> The eastern boundary of the Kermadec plate is also the site of the Kermadec Trench, which is the fifth deepest trench in the world at about 10,000 m.<ref name=":2" /> The eastern boundary of the Tonga plate is one of the fastest subduction zones with a rate of up to {{cvt|24|cm/year}}.<ref name=":1">{{Cite journal|last1=Smith|first1=Ian E. M.|last2=Price|first2=Richard C.|date=2006-09-01|title=The Tonga–Kermadec arc and Havre–Lau back-arc system: Their role in the development of tectonic and magmatic models for the western Pacific|journal=Journal of Volcanology and Geothermal Research|series=Silicic Volcanism and Crustal Evolution in Oceanic Arcs|volume=156|issue=3|pages=315–331|doi=10.1016/j.jvolgeores.2006.03.006|bibcode=2006JVGR..156..315S}}</ref>
==Creation==
The Tonga and Kermadec plates originated about 4-5 million years ago.<ref name=":0" /> Before their creation, the Pacific plate was subducting under the Australian plate, producing the [[Lau-Colville Ridge]] (now extinct).<ref name=":1" /> About 6 million years ago, this region underwent [[crustal extension]] and through a complicated series of spreading centers, ultimately leading to the separation of the Pacific and Australian plate and the creation of what are now Tonga and Kermadec plates.<ref name=":1" /> The Tonga and Kermadec plates separated because the northern portion of the original plate was growing much more quickly at {{cvt|9.6|cm/year}} than the southern portion at {{cvt|3.9|cm/year}}, eventually generating a transform fault between them, creating the Tonga and Kermadec plates.<ref name=":3">{{Cite journal|last1=Zellmer|first1=Kirsten E.|last2=Taylor|first2=Brian|date=2001-05-01|title=A three-plate kinematic model for Lau Basin opening|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=2|issue=5|pages=1020|doi=10.1029/2000gc000106|issn=1525-2027|bibcode=2001GGG.....2.1020Z|doi-access=free}}</ref> Just as this phenomenon created the Tonga and Kermadec plates, it was also the cause of the creation of the Niuafo’ou microplate to the northwest of the Tonga plate because the Tonga's northern portion is still growing much faster than the southern counterpart.<ref name=":3" />
==Volcanism==
There is extensive and currently active arc volcanism including the volcanoes of [[List of volcanoes in Tonga|Tonga]], the [[Kermadec Islands]], the [[South Kermadec Ridge Seamounts]] and the [[Taupō Volcanic Zone]].
=="Kermadec Sanctuary"==
With the largest underwater volcano chain, the region surrounding the Kermadec–Tonga subduction zone is one of the most geologically diverse areas in the world.<ref name=":4">{{Cite web|url=http://www.mfe.govt.nz/marine/kermadec-ocean-sanctuary/about-sanctuary|title=About the Kermadec Ocean Sanctuary {{!}} Ministry for the Environment|website=mfe.govt.nz|language=en-NZ|access-date=2017-06-09}}</ref> The Kermadec Sanctuary was proposed in 2015 by the Prime Minister of New Zealand, [[John Key]], at the United Nations in New York, which would create an area off limits to aquaculture, fishing, and mining.<ref>{{Cite web|url=http://www.stuff.co.nz/environment/93065599/david-tong-ending-threats-to-maui-dolphins-would-show-nz-keeps-its-promises|title=David Tong: Ending threats to Maui dolphins would show NZ keeps its promises|website=Stuff|date=30 May 2017 |access-date=2017-06-09}}</ref> The sanctuary would be 620,000 square kilometers, making it the world's largest and most significant fully protected areas.<ref name=":4" /> The intention was to have the sanctuary in place, enacted by Parliament in November 2016.<ref name=":4" /> In September 2016, the enactment of the Kermadec Sanctuary was delayed due to failed negotiations over the [[Māori people|Māori people's]] rights.<ref>{{Cite web|url=http://www.stuff.co.nz/national/politics/84249268/kermadec-sanctuary-legislation-to-be-delayed-after-failed-negotiations-over-maori-rights|title=Kermadec sanctuary legislation to be delayed after failed negotiations over Maori rights|website=Stuff|access-date=2017-06-09}}</ref> As of June 2017, these issues have still not been resolved.
==See also==
* [[Tonga–Kermadec Ridge]]
* [[Tonga Trench]]
* [[Kermadec Trench]]
* [[Lau Basin]]
* [[Havre Trough]]
* [[Hunga Tonga–Hunga Haʻapai]]
==References==
{{reflist}}
==External links==
* https://web.archive.org/web/20110717144745/http://www.ifm-geomar.de/div/projects/zealandia/english/maps.html
* http://www.teara.govt.nz/EarthSeaAndSky/OceanStudyAndConservation/SeaFloorGeology/2/en
{{coord missing}}
[[Category:Plate tectonics]]
[[Category:Subduction zones]]
[[Category:Geographic areas of seismological interest]]
[[Category:Geology of New Zealand]]
[[Category:Seismic faults of New Zealand]]
[[Category:Volcanism of New Zealand]]
[[Category:Seismic zones of Oceania]]